late bloomer
US /leɪt ˈbluːmər/
UK /leɪt ˈbluːmər/

1.
a person whose talents or capabilities are not recognized or developed until later than usual
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He was a late bloomer in his career, finding success in his forties.
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Many creative geniuses are often considered late bloomers.
2.
a plant that flowers later in the season than is typical for its species
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These roses are late bloomers, they won't flower until autumn.
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The garden features several beautiful late bloomers that provide color into winter.